Combined vaccine-immune-checkpoint inhibition constitutes a promising strategy for treatment of dMMR tumors

Inken Salewski,Claudia Maletzki,Steffen Kuntoff,Christian Junghanss,Andreas Kuemmel,Stephan B Felix,Rico Feldtmann,Larissa Henze

doi:10.1007/s00262-021-02933-4

Abstract

BackgroundMlh1-knock-out-driven mismatch-repair-deficient (dMMR) tumors can be targeted immunologically. By applying therapeutic tumor vaccination, tumor growth is delayed but escape mechanisms evolve, including upregulation of immune-checkpoint molecules (LAG-3, PD-L1). To counteract immune escape, we investigated the therapeutic activity of a combined tumor vaccine-immune-checkpoint inhibitor therapy using α-PD-L1.DesignIn this trial, Mlh1-knock-out mice with established gastrointestinal tumors received single or thrice injections of α-PD-L1 monoclonal antibody clone 6E11 (2.5 mg/kg bw, q2w, i.v.) either alone or in combination with the vaccine. Longitudinal flow cytometry and PET/CT imaging studies were followed by ex vivo functional immunological and gene expression assays.Results6E11 monotherapy slightly increased median overall survival (mOS: 6.0 weeks vs. control 4.0 weeks). Increasing the number of injections (n = 3) improved therapy outcome (mOS: 9.2 weeks) and was significantly boosted by combining 6E11 with the vaccine (mOS: 19.4 weeks vs. 10.2 weeks vaccine monotherapy). Accompanying PET/CT imaging confirmed treatment-induced tumor growth control, with the strongest inhibition in the combination group. Three mice (30%) achieved a complete remission and showed long-term survival. Decreased levels of circulating splenic and intratumoral myeloid-derived suppressor cells (MDSC) and decreased numbers of immune-checkpoint-expressing splenic T cells (LAG-3, CTLA-4) accompanied therapeutic effects. Gene expression and protein analysis of residual tumors revealed downregulation of PI3K/Akt/Wnt-and TGF-signaling, leading to T cell infiltration, reduced numbers of macrophages, neutrophils and MDSC.ConclusionsBy successful uncoupling of the PD-1/PD-L1 axis, we provide further evidence for the safe and successful application of immunotherapies to combat dMMR-driven malignancies that warrants further investigation.

Highlights

Mlh1-knock-out-driven mismatch-repair-deficient tumors can be targeted immunologically
CTLA4, PD-1, or PD-L1 are the so far most studied checkpoint molecules and immune-checkpoint inhibitors (ICI) widely applied in the clinic to improve
Atezolizumab, Avelumab and Durvalumab are FDA approved as PD-L1 blocking antibodies

Summary

Introduction

Mlh1-knock-out-driven mismatch-repair-deficient (dMMR) tumors can be targeted immunologically. By applying therapeutic tumor vaccination, tumor growth is delayed but escape mechanisms evolve, including upregulation of immune-checkpoint molecules (LAG-3, PD-L1). We investigated the therapeutic activity of a combined tumor vaccine-immune-checkpoint inhibitor therapy using α-PD-L1. A hallmark of dMMR tumors – irrespective of organ manifestation – is an ultramutated tumor phenotype (= TMB high), leading to a high abundance of frameshifted neo-epitopes on the tumor cells’ surface This latter feature underlines the tremendous potential for immunological targeting of dMMR cancers [15,16,17]. To counteract vaccination-induced immune escape and improve overall survival, we here applied a murine α-PD-L1 antibody (clone: 6E11) in combination with repeated vaccination

Results

Discussion

Conclusion